1. Field of the Invention
The invention relates to a chip resistor comprising a chip type insulating substrate with a thin-film resistance provided thereon. More specifically, the invention is intended to provide a chip resistor provided with a resistance or electrodes that will not be lost upon coming in contact with human sweat or seawater.
2. Description of the Related Art
Conventional chip resistors include a thick-film resistor provided with electrodes and a resistance, formed by printing and firing constituent materials thereof, and a thin-film resistor provided with electrodes and a resistance, formed by sputtering constituent materials thereof. Both are substantially same in construction although they differ from each other in that one is formed of a thick-film while the other is formed of a thin-film, and in respect of vertical relationship between the resistance and upper electrodes. That is, as shown in FIG. 9, at opposite ends of an insulating substrate 1 made of alumina, and so forth, there are provided a pair of electrodes 2, 3, formed of upper surface electrodes 21, 31, back surface electrodes 22, 32, and side surface electrodes 23, 33, respectively, the side surface electrodes 23, 33 connecting the upper surface electrodes with the back surface electrodes, respectively, and a resistance 4 is formed on top of the insulating substrate 1 in such a way as to be connected to both the electrodes 2, 3. A protection film 5 in one to three layers is formed on the top surface side of the resistance 4.
The thick-film resistor is obtained by forming respective layers by applying a constituent material, reduced to a paste form with the use of glass or resin, to a substrate by printing and so forth, and subsequently, by firing the constituent material (in the case of glass) at a temperature in the range of 600 to 900° C. or curing the constituent material (in the case of resin) at a temperature in the range of 200 to 240° C. For the constituent material of electrodes, use is made of an Ag based metal paste with Pd added to Ag or an Au based metal paste with Au as the primary constituent thereof, and for the constituent material of a resistance, use is made of ruthenium oxide (RuO2) with Ag, and so forth, mixed therewith, for obtaining a necessary resistance value, and reduced to a paste form with the use of glass or resin. The thin-film resistor is obtained by forming films by means of, for example, sputtering metallic materials, and patterning the films, and for the constituent material of electrodes, use is made of Al, Ni, Cr, Cu, and so forth while for the constituent material of a resistance, use is made of Ni—Cr alloy, and so firth,
Herein, the thick-film refers to a film formed by applying the constituent material of electrodes or a resistance, reduced to a paste form, to a substrate, and subsequently, by firing or curing the same while the thin-film refers to a film formed by directly forming a metal film, and so forth, by the sputtering method and so forth.
Now, in order to obtain a high-precision chip resistor, a resistance needs to be formed of a thin film, and chip resistors (thin-film chip resistors), using thin films made of Ni—Cr for a resistance and side electrodes, have been extensively fabricated. Such thin-film resistors, however, have a problem in that if, for example, human sweat, seawater, etc. are adhered thereto, there occurs chemical reaction between NaCl contained in human sweat, seawater, etc. and Ni—Cr due to presence of moisture, thereby causing the thin films made of Ni—Cr to be lost.
In such a case, as for the resistance, a constituent material other than Ni—Cr, not reacting with NaCl etc., can be selected, however, for the side electrodes, use of Ni—Cr or Ni—Ti is unavoidable in view of such problems as resistivity and oxidation, so that it has been impossible to resolve the problem described above.
The invention has been developed to resolve the problem described above, and it is an object of the invention to provide a chip resistor of a construction capable of maintaining accuracy of a resistance value, and protecting side electrodes from being lost due to reaction of the side electrodes with moisture as well as NaCl etc., contained in human sweat, and so on, and a method of fabricating the same. Further, the invention is intended to provide a chip resistor capable of coping with deterioration in tackiness, occurring when a thick-film is formed on top of a thin-film.